In metal connection in electrical and electronic devices or the like, solder connection using a solder paste has been generally used and in such a solder paste, a solder alloy containing lead has been conventionally used.
However, in view of environmental load, the use of lead has been recently required to be suppressed and thus, the development of a solder alloy without containing lead (lead-free solder alloy) has been promoted.
As such a lead-free solder alloy, for example, a tin-copper alloy, a tin-silver-copper alloy, a tin-silver-indium-bismuth alloy, a tin-bismuth alloy, and a tin-zinc alloy have been well known and among all, a tin-silver-copper alloy, a tin-silver-indium-bismuth alloy, and the like have been widely used.
Meanwhile, silver contained in the tin-silver-copper alloy is very expensive, so that a reduction of the silver content is required in terms of cost reduction. Also, the solder alloy is required to have excellent connection strength (cooling/heating fatigue resistance or the like).
In order to satisfy such requirement, for example, a tin-silver-copper solder alloy, that is, a solder alloy which consists of tin, silver, copper, nickel, antimony, bismuth, and indium; does not contain germanium except for germanium contained in impurities that are inevitably mixed; has the content ratio of the silver of above 0.05 mass % and below 0.2 mass %, the content ratio of the copper of 0.1 mass % or more and 1 mass % or less, the content ratio of the nickel of 0.01 mass % or more and 0.2 mass % or less, the content ratio of the antimony of 0.01 mass % or more and below 2.5 mass %, the content ratio of the bismuth of 0.01 mass % or more and 4 mass % or less, the content ratio of the indium of 0.005 mass % or more and 2 mass % or less, and the content ratio of the tin of the remaining ratio with respect to the total amount of the solder alloy; and has the mass ratio (Cu/Ni) of the copper content with respect to the nickel content of below 12.5 has been proposed (ref: for example, Patent Document 1).
According to the solder alloy, a cost reduction can be achieved and excellent connection strength (cooling/heating fatigue resistance or the like) can be also obtained.